Apparatus for injecting a sample into a gas chromatograph

ABSTRACT

An apparatus for introducing a liquid sample into a gas chromatograph, including a heated housing having located therein a liquid sample evaporation chamber and a gauge pressure chamber and further incorporating means for establishing a pressure differential between the gauge pressure chamber and the evaporation chamber. The liquid sample evaporation chamber is hermetically sealed from the ambient atmosphere and communicates with the source of supply of a carrier gas of the associated gas chromatograph and with the separation column of the same chromatograph. The gauge pressure chamber communicates with the said carrier gas supply source. Each one of the two chambers has an opening tightly closed with a gasket made of an elastic material and intended for introduction thereinto of a needle having two pointed ends and bent so that these two pointed ends extend parallel to each other in the same direction. The needle has an internal longitudinal capillary passage open at both ends, adapted to be filled with a liquid sample that can be transferred into the sample evaporation chamber, after the respective two ends of the needle have pierced the gaskets of the two chambers, the sample being transferred under the action of the pressure differential between the gauge pressure chamber and the evaporation chamber.

Waited @tates Patent 1 Chizhov et al.

[451 May 29, W73

[ APPARATUS FOR HNJECTING A [57] ABSTRACT SAMPLE INTO A GAS CHROMATOGRAPH An apparatus for introducing a liquid sample into a gas chromatograph, including a heated housing having [76] Inventors: Leonid Viadlimirovich Chizhov, located therein a liquid sample evaporation chamber Leninsky prospekt, 82/2, kv. 362; and a gauge pressure chamber and further incorporat- Dmitry Emelyanovich Lengauer, ing means for establishing a pressure differential Bolshaya Ugreshskaya ulitsa, between the gauge pressure chamber and the evapora- 'g Alexafldlovich 1 tion chamber. The liquid sample evaporation chamber Ambulatomy Proezd, 2/6, all is hermetically sealed from the ambient atmosphere of Moscow and communicates with the source of supply of a car- 22 Filed; Man 0 19 2 rier gas of the associated gas chromatograph and with the separation column of the same chromatograph. [21] Appl' 233525 The gauge pressure chamber communicates with the said carrier gas supply source. Each one of the two [52] [1.8. CI. ..73/422 GC, 73/425.4 P chambers h an p ni g gh ly closed wi h a g ke [51] int. Cl. .1301] 3/02, GOln 1/10 made of an elastic material and intended for introduc- [58] Field of Search ..73/421 B, 422 GC, tion thereinto of a needle having two pointed ends and 73/23.1; 141/329, 425.4 P bent so that these two pointed ends extend parallel to each other in the same direction. The needle has an [56] References Cited internal longitudinal capillary passage open at both ends, adapted to be filled with a liquid sample that can UNITED STATES PATENTS be transferred into the sample evaporation chamber, 2,991,647 7/1961 Harris ..73/422 GC after the respective two ends of the needle have 3,327,520 /1 67 appJr- C pierced the gaskets of the two chambers, the sample 3,604,267 9/1971 Johns ..73/422 GC Primary Examiner-S. Clement Swisher Attorneyl-lolman & Stern being transferred under the action of the pressure differential between the gauge pressure chamber and the evaporation chamber.

APPARATUS FOR INJECTING A SAMPLE INTO A GAS CHROMATOGRAPH The present invention relates to chromatography, and, more particularly, it relates to apparatus for injecting a liquid sample into a gas chromatograph; it can be used in the chemical, petrochemical, food and other industries.

There is known an apparatus for injecting a liquid sample into a gas chromatograph, comprising a heated unit accommodating therein a liquid sample evaporation chamber hermetically sealed from the ambient atmosphere and communicating, on the one hand, with a source of supply of a carrier gas into the gas chromatograph and, on the other hand, with the separation column of the same gas chromatograph, this chamber having an opening tightly closed with a gasket made of an elastic material, this opening being means for introduction of a needle into this chamber. The needle has one pointed end and internal longitudinal capillary passage open at both ends of the needle, adapted to accomodate therein a liquid sample to be introduced into the evaporation chamber.

In this known apparatus a microsyringe is employed as a metering member, the needle of the microsyringe being in the form of a capillary tube with a calibrated passage, one end of the needle being pointed. The end of the needle, opposite to the pointed one, is connected with the housing of the microsyringe, the housing receiving thereinside a reciprocating rod connectedwith a calibrated-diameter wire reciprocating within the passage of the needle, the wire acting as a reciprocating plunger for drawing a sample into the needle and forcing the sample therefrom into the sample evaporation chamber.

To introduce a liquid sample, the needle of the microsyringe pierces by its pointed end the gasket made of an elastic material and thus enters the evaporation chamber, whereafter the rod of the microsyringe is depressed, and the sample is forced from the internal passage of the needle into the evaporation chamber. The volume of the sample which is being introduced is determined by the travel of the rod along a metering scale provided on the housing of the microsyringe.

The presence in the microsyringe of movable parts and parts subject to friction substantially reduces the service life of the microsyringe; furthermore, a clearance which is always left between the calibrateddiameter wire and the walls of the internal passage of the needle results in poor sealing.

Because of poor tightness, the accuracy of introduction and reproducibility of a liquid sample are decreased, particularly, in cases when the sample is to be introduced into an evaporation chamber operated under elevated pressure.

Because of poor lightness in the saidapparatus it is also difficult to fall up the internal passage of the needle with a liquid sample preventing air access thereinto.

When microsyringe includes movable parts and parts subject to friction, it is impossible to employ the microsyringe for injection of liquid samples containing unsoluble suspended matter, as well as of aggressive liquids which cause corrosion of the parts of the microsyringe.

Among the other disadvantages of the abovedescribed known apparatus, that also affect the accuracy of sample injection and reproducibility, is the presence of dead volume within the clearance between the calibrated-diameter wire and the walls of the internal passage of the needle of the microsyringe, this dead volume being liable to grow, as the part subject to friction are wearing out in operation. When the needle is introduced into the sample evaporation chamber, that portion of the sample which fills this dead volume evaporates, meanwhile, it is difficult to calculate the volume of this evaporated portion, since it depends on such variables as the size of the clearance between the calibrated wire and the internal wall of the passage of the needle, the composition of the mixture to be analyzed, the temperature of the evaporation chamber, the flow rate of the carrier gas, the time during which the needle is in the evaporation chamber.

The abovementioned disadvantages of the known apparatus for injecting a liquid sample into a gas chromatograph limit the field of its application and its service life; they affect the accuracy of sample introduction and reproducibility as much as from several per cent to several dozen per cent. Moreover, the smaller is the volume of the sample to be introduced, the poorer is the accuracy.

It is an object of the present invention to provide an apparatus for injecting a liquid sample into a gas chromatograph, which ensures high accuracy of introduction and reproducibility of the liquid samples in the volume from 0.1 to 10 p. up to :1 percent accuracy.

It is another object of the present invention to provide an apparatus for injecting a liquid sample into a gas chromatograph, which permits injecting accurately metered and reproducible volumes of samples into the sample evaporation chamber of a gas chromatograph, operated under an elevated pressures.

It is still another object of the present invention to provide an apparatus for injecting a liquid sample into a gas chromatograph, which offers quick and simple filling of the needle with a liquid sample and injecting the sample into the evaporation chamber.

With these and other objects in view, the present invention resides in an apparatus for injecting a liquid sample into a gas chromatograph, comprising a heated housing inside which there is located a liquid sample evaporation chamber hermetically sealed from the ambient atmosphere and communicating, on the one hand, with the source of supply of a carrier gas into said chromatograph and, on the other hand, with the separation column of the same said gas chromatograph, said chamber having an opening tightly closed with a gasket made of an elastic material and intended to be pierced by a needle, said needle having a pointed end and a longitudinal internal capillary passage open at both ends of said needle, said passage being adapted to be filled with a liquid sample, said apparatus, in accordance with the present invention, further incorporating a gauge pressure chamber located within said heated housing and communicating with said source of supply of said carrier gas, and means for establishing a pressure differential between said gauge pressure chamber and said liquid sample evaporation chamber, said needle having the other end thereof also pointed, said needle being bent so that said two pointed ends thereof extend parallel to each other in the same direction, said gauge pressure chamber also having an inlet for introduction of said needle into said gauge pressure chamber, said last-mentioned inlet being tightly closed with another gasket made of an elastic material, so that both said gaskets of said two respective chambers are adapted to be simultaneously pierced by the respective ones of said two pointed ends of said needle, whereby said liquid sample accomodated in said capillary passage of said needle can be transferred therefrom into said liquid sample evaporation chamber under the action of said pressure differential established between said gauge pressure chamber and said liquid sample evaporation chamber.

It is advisable that said gaskets of both said chambers, made of said elastic material, should be in the form of a single plate, common to both said chambers.

It is further advisable that said means for establishing a pressure differential between said gauge pressure chamber and said liquid sample evaporation chamber should be in the form of a capillary passage establishing communication between said two chambers.

Alternatively, said means for establishing a pressure differential between said gauge pressure chamber and said liquid sample evaporation chamber may be in the form of a pressure differential regulator having an input pressure connection, a reference pressure connection and an output pressure connection, communicating with said carrier gas supply source, with said liquid sample evaporation chamber and said gauge pressure chamber respectively.

It may be advisable to have the gauge pressure chamber communicating with the ambient atmosphere through an auxiliary capillary passage.

Preferably, said needle has the bent portion thereof clamped in a holder, so that said two pointed ends thereof project from the face end of said holder parallel to each other by the same distance.

An apparatus for introducing a liquid sample into a gas chromatograph being of a structure embodying the present invention, it provides for a practically unlimited period of time, high accuracy of introduction of a sample and reproducibility of its volume at both normal and relatively high pressures within the sample evaporation chamber; it prolongs the service life of the needle; it is both simple and reliable in operation; it is capable of introducing samples including solid unsoluble particles and samples of aggressive liquids and liquids displaying polymerization in contact with the ambient air.

The present invention will be further described in connection with two embodiments thereof, with reference being has to the accompanying set of drawings, wherein:

FIG. 1 is a longitudinal sectional view of an apparatus for introducing a liquid sample into a gas chromatograph, embodying the present invention;

FIG. 2 is a longitudinal sectional view of an alternative embodiment of the present invention;

FIG. 3 illustrates the general view of a holder clamping therein the needle of the apparatus for introducing a liquid sample into a gas chromatograph, embodying the invention;

FIG. 4 shows the general view of an exemplary set of needles to be used in the apparatus for introducing a liquid sample into a gas chromatograph, embodying the invention.

An apparatus for introducing a liquid sample into a gas chromatograph constructed in accordance with both alternative embodiments of the present invention, to be described hereinbelow, comprises a housing 1 (FIGS. 1 and 2) associated with a heating member (not shown in the drawings), the housing having therein a cylindrical chamber 2 for evaporation of a liquid sample and a cylindrical gauge pressure chamber 3, the axes of the two chambers extending parallel to each other.

The liquid sample evaporation chamber 2 communicates, on the one hand, with a source of carrier gas to be supplied to the associated chromatograph, via a control valve 4, and, on the other hand, with the separation chromatographic column of the same chromatograph (the carrier gas source and the separation column of the gas chromatograph are not shown in the appended drawings). In accordance with the first-described embodiment of the present invention, illustrated in FIG. 1, the liquid sampled evaporation chamber 2 communicates with the carrier gas supply source through the gauge pressure chamber 3, whereas in accordance with the second alternative embodiment of the invention, shown in FIG. 2, the liquid sample evaporation chamber 2 directly communicates with the carrier gas source.

The chambers 2 and 3 (FIGS. 1 and 2) have at the respective adjacent ends thereof openings through which a needle 5 can be introduced thereinto, the two openings being closed with a gasket made of an elastic material, e.g. of silicone rubber, the gasket being common to the two openings and being in the form of a panel 4. The panel 6 is secured by a strip 7 pressing the panel to the housing 1, the strip 7 having guiding apertures 8 made therethrough and being held in place by a nut 9. The nut 9 is finned to effect cooling of the upper portion of the housing 1, where the elastic panel 6 is received.

The needle 5 is bent in such a manner that the two ends thereof are parallel to each other and extend in the same direction, both ends 10 of the needle pointed. A capillary passage 11 extends longitudinally throughout the entire length of the needle 5 (FIG. 3) and is open at both pointed ends 10 thereof, the passage being adapted to be filled with a liquid sample to be introduced into the liquid sample evaporation chamber 2. In the herein disclosed embodiments of the present invention the needle 5 is generally U-shaped.

The bent portion of the needle 5 (FIG. 3) is clamped in a holder 12, so that both pointed ends 10 of the needle project from the holder 12 by the same distance and are parallel to each other. The holder 12 is in the form of a rod having made therein a longitudinal slot 13 receiving therein the needle 5, the needle being clamped in the slot under the action of a securing screw 14.

The respective gaskets of the two chamber 2 and 3 (FIG. 1 and 2) are formed, as it has been already mentioned, by the common panel 6 closing the two adjacent face ends of the two chambers, so that the panel 6 is adapted to be pierced simultaneously by the two pointed ends of the needle 5.

In accordance with both alternative embodiments of the present invention, an apparatus for introducing a liquid sample into a gas chromatograph further incorporates means for creating a pressure differential between the gauge pressure chamber 3 and the liquid sample evaporation chamber 2.

In accordance with the first-described embodiment (FIG. I) particularly adapted to be incorporated in chromatographs with isothermic operation of the separation columns, the means for establishing a pressure differential between the gauge pressure chamber 3 and the sample evaporation chamber 2 is in the form of a capillary passage 15 establishing communication between the two chambers 2 and 3.

In accordance with the second alternative embodiment of the present invention (FIG. 2), particularly adapted for incorporation in chromatographs with isothermic and program controlled operating condition of the separation column, the means for creating a pressure differential between the gauge pressure chamber 3 and the sample evaporation chamber 2 is in the form of a pressure differential regulator 16 in which the input, reference and output pressure connections 17, 18 and 19 communicate with the carrier gas supply source, the liquid sample evaporation chamber 2 and with the gauge pressure chamber 3 respectively. The value of the pressure differential between the chambers 2 and 3 can be preset with the help of an adjustment screw 20 and a compression spring 21 acting upon a control diaphragm 22.

According to both herein described embodiments of the present invention FIGS. 1 and 2) the gauge pressure chamber 3 communicates with the ambient atmosphere via a capillary passage 23, the chamber 3 communicating with the carrier gas supply source either directly (as in the first-described embodiment, FIG. ll), or through the pressure differential regulator 16 (as in the second embodiment, FIG. 2). According to both embodiments, the liquid sample evaporation chamber 2 is hermetically sealed from the ambient atmosphere.

FIG. 4 of the appended drawings illustrates a set of replaceable needles 5 employed in the herein disclosed apparatus as metering members having the respective volumes of their capillary passages 11 within a range from 0.1 [Ll to pl the appropriate one of the set of the needles being selected to correspond to the aim of an analysis and to the type of the separation columns employed.

The operation principle of the herein disclosed apparatus for introducing a liquid sample into a gas chromatograph is the same for both embodiments of the present invention and will be described in detail hereinbelow in connection with the first embodiment, illustrated in FIG. 1.

To create a pressure differential between the gauge pressure chamber 3 and the liquid sample evaporation chamber 2, the carrier gas is fed from the supply source through the control valve 4 (FIG. 1) in the direction of the arrow line A into the gauge pressure chamber, 3 wherefrom it flows through the capillary passage 15 into the liquid sample evaporation chamber 2, whereafter the gas flows in the direction of the arrow line B into the associated separation column A desired rate of flow of the carrier gas, to satisfy the operation of the chromatographic column, is preset by means of the control valve 4. The two chambers 2 and 3 being connected in the gas path in series, via the capillary passage 15 presenting resistance to the carrier gas flow, the pressure within the chamber 3 is higher than that within the chamber 2, Le. there is created a pressure differential between the chambers 2 and 3.

As the following step of the operation, the needle 5 of the appropriate volume is selected from the set of replaceable needles illustrated in FIG. 4.

The selected needle 5 (FIG. 3) is put into the longitudinal slot of the holder 12 and clamped with the help of the screw 14. To fill the internal capillary passage 11 of the needle 5 with the liquid to be analyzed, it is sufficient to touch the surface of the liquid with any one of the pointed ends 10 of the needle 5. Complete filling of the passage 11 with the liquid is due to the capillary action. To fill the capillary passage 11 of the needle 5 either with a liquid that would not wet the surface of the walls of the passage, or else with a highly viscous liquid, forced filling of the passage 11 of the needle 5 should be resorted to.

The operation of introducing the sample into the evaporation chamber 2 (FIG. 1) is effected by moving the holder 12 with the needle 5 clamped therein in the direction of the arrow line C, by introducing the pointed ends 10 of the needle 5 into the respective guiding apertures 8 of the strip 7 and piercing the elastic panel 6 with these pointed ends 1th, whereby one of the two pointed ends 10 of the needle 5 finds itself within the liquid sample evaporation chamber 2, and the other one of the pointed ends finds itself within the gauge pressure chamber 3.

Owing to the pressure differential maintained, as it has been already described, between the chambers 2 and 3, the liquid sample is rapidly forced from the internal passage 11 of the needle 5 into the sample evaporation chamber 2. Now the pointed ends 10 of the needle 5 may be withdrawn from the chambers 2 and 3, respectively, by the holder 12 being pulled in the direction of the arrow line D. In its turn, the liquid sample in the form of vapor is carried in the flow of the carrier gas into the associated separation chamber of the gas chromatograph.

Following in the wake of the liquid sample, a small amount of the carrier gas finds its way from the gauge pressure chamber 2 into the sample evaporation chamber 3. However, the pressure differential between the two chambers 2 and 3 being but slight (about 0.1 atrn.), the needle 5 exhibiting relatively high gas flow resistance (the ratio of the length of the needle to the internal diameter thereof being high), the needle 5 being left within the two chambers 2 and 3 for but a very short time, the volume of the carrier gas that occurs in the sample evaporation chamber 2 is hardly in excess of several tenths of a ml which particularly does not interfere with the operational duty of the chromatograph.

The pressure rise pulse which is created in this manner at the inlet of the separation column does not excede a pressure rise pulse that is brought about by the introduction of several tenths of a ,ul of the sample, introduced by any other known method, as the liquid sample is transformed into vapor.

The permanent flow of the carrier gas through the gauge pressure chamber 3 into the ambient atmosphere through the capillary outlet passage 23 washes away any traces of he sample, that may have been introduced into the chamber 3 on the external surface of the respective end 10 of the needle 5.

Should such need arise, the internal passage 1 1 of the needle 5 may be flushed with an appropriateorganic solvent, to wash away the traces of the preceding sample. To achieve this, the capillary passage 1 1 of the needle 5 is filled with the solvent in a manner similar to that of filling the passage with a liquid sample, whereafter either one of the pointed ends 10 of the needle 5 is introduced into the gauge pressure chamber 3 through the panel 6, while the other end 110 of the needle 5 is left in the ambient air (this position is not illustrated in the appended drawings). The gauge pressure within the chamber 3 in this case forces the solvent out from the internal passage 11 of the needle into the ambient air. A single flushing of this kind is sufficient to make the internal surface of the needle entirely free from the traces of the preceding sample, and the needle 5 is thus prepared for introducing a liquid sample of a different composition.

The operation of the apparatus for introducing a liquid sample into a gas chromatograph, constructed in accordance with the second embodiment of the present invention, is quite similar to the abovedescribed operation of the first embodiment, except the way in which the pressure differential is created between the chambers 2 and 3.

According to the second embodiment of the present invention (FIG. 2), in the apparatus for introducing a liquid sample into a gas chromatograph the pressure differential between the chambers 2 and 3 is established, as follows.

The carrier gas from the supply source is directed along two paths. Following one of the paths, the gas passes through the control valve 4 and enters the sample evaporation chamber 2 in the direction the arrow line A, wherefrom it flows in the direction of the arrow line B into the separation chromatographic chamber of the gas chromatograph. The control valve 4 is set to a desired rate of flow of the carrier gas through the chromatographic column, and the pressure of the carrier gas established within the liquid sample evaporation chamber 2 acts upon the control diaphragm 22 of the pressure differential regulator 16 through the reference pressure connection 18 thereof. Following the other one of the two paths, a flow of the carrier gas from the carrier gas supply source enters the inlet pressure connection 17 of the pressure differential regulator 16, wherefrom it flows through the outlet pressure connection 19 into the gauge pressure chamber 3. An increase of the pressure within the chamber 3 over that established within the chamber 2 (ie a desired pressure differential between the chambers 3 and 2) is in this case established by exerting an additional mechanical pressure upon the diaphragm 22 with the held of the adjustment screw 20 and the compression spring 21.

However, it should be understood that the abovedescribed embodiments of the invention are meant but to illustrate the principal features of the invention, and they are in no way intended to limit the scope thereof by excluding other possible modifications within the general aspects of the invention.

The herein disclosed apparatus for introducing a liquid sample into a gas chromatograph provides for a high accuracy of introduction and reproducibility (within :1 percent), when a small-volume (0.1 to #1) liquid sample is introduced into the separation column of a gas chromatograph.

The incorporation in the herein disclosed apparatus of a chamber where the pressure is maintained positively above the within the sample evaporation chamber has made it possible to employ as a metering member of the apparatus a needle of a bent shape, which is exclusively simple both in manufacture and handling, the needle having a capillary passage open at both ends. The herein disclosed apparatus has no moving parts and parts subject to friction, as well of dead volume, whereby the herein disclosed apparatus is capable of offering stable characteristics within long periods of operation.

Furthermore, the herein disclosed apparatus offers introduction of liquid samples with unaffected accuracy into an evaporation chamber maintained under a high pressure, e.g. in cases of employment of separation chambers with a high gas flow resistance and columns operable at high pressures.

The operation of filling the metering volume of the needle with a liquid sample and introducing the sample into the sample evaporation chamber with the employment of the herein disclosed apparatus is both simple and swift. The herein disclosed apparatus can be successfully used for introduction of aggressive substances and compositions displaying polymerization in contact with the ambient air.

Should the metering device of the herein disclosed apparatus is either clogged or broken, it can be easily and quickly replaced by another one from a spares set. The process of production of bent needles from capillary tubes having internal volume from 0.1 ,ul to 10 ul is extremely simple, and the cost of the needles is very low in comparison with that of microsyringes. Taking into consideration the limited service life of microsyringes, it becomes evident that the employment of the herein disclosed apparatus for introducing a liquid sample into a gas chromatograph offers both money savings and greater efficiency.

Moreover, the herein disclosed apparatus may be employed in other cases where a small volume of a liquid is to be introduced into an instrument with a sufficiently high accuracy, e.g. into the vacuum system of a mass-spectrometer.

What is claimed is:

1. An apparatus for introduction of a liquid sample into a gas chromatograph, comprising: a housing; a heating means associated with said housing for heating same; a chamber for evaporation of said liquid sample within said housing; said liquid sample evaporation chamber being hermetically sealed from the ambient atmosphere and communicating, on the one hand, with a source of supply of a carrier gas into said gas chromatograph, and, on the other hand, with the separation column of the said gas chromatograph; a gauge pressure chamber also situated within said housing and communicating with said carrier gas supply source; means for creating a pressure differential between said gauge pressure chamber and said liquid sample evaporation chamber; said liquid sample evaporation chamber having a first opening; a first gasket made of an elastic material closing said first opening; said gauge pressure chamber having a second opening; a second gasket of an elastic material closing tightly said second opening; a needle having both its ends pointed, said needle being bent so that said two ends thereof extend parallel to each other and extend in the same direction, said needle being adapted to be introduced into said sample evaporation chamber and into said gauge pressure chamber, respectively, through said first and said second gaskets closing said first and said second opening; said needle having made therein a longitudinal internal capillary passage open at both said ends and adapted to be filled with said liquid sample; said needle being adapted to be introduced into said sample evaporation chamber and said gauge pressure chamber through, respectively, said first and said second gaskets so that said first and said second gaskets associated with said respective chambers are pierced simultaneously by the said respective pointed ends of said needle, establishing conditions for transfer of said liquid sample from said passage of said needle into said sample evaporation chamber under the action of said pressure differential maintained between said gauge pressure chamber and said sample evaporation chamber.

2. An apparatus according to claim 1, wherein said first and said secondv gaskets made of said elastic material and associated, respectively, with said liquid sample evaporation chamber and said gauge pressure chamber are formed by a single panel, common to both said gaskets.

. 3. An apparatus according to claim 1, wherein said means for establishing a pressure differential between said gauge pressure chamber and said sample evaporation chamber includes a capillary passage establishing communication between said chambers.

4. An apparatus according to claim 1, wherein said means for establishing a pressure differential between said gauge pressure chamber and said sample evaporation chamber includes a pressure differential regulator having an input pressure connection, a reference pressure connection and output pressure connection communicating, respectively, with said carrier gas supply source, with said sample evaporation chamber and with said gauge pressure chamber.

5. An apparatus according to claim ll, wherein said gauge pressure chamber communicates with the ambient atmosphere through an additional capillary passage.

6. An apparatus according to claim 1, wherein said needle has the bent portion thereof clamped into a holder so that said pointed ends thereof project from the face end of said holder by equal distances, parallel to each other. 

1. An apparatus for introduction of a liquid sample into a gas chromatograph, comprising: a heated housing; a chamber for evaporation of a liquid sample within said housing, said liquid sample evaporation chamber being hermetically sealed from the ambient atmosphere and communicating, on the one hand, with a source of supply of a carrier gas into said gas chromatograph, and, on the other hand, with a separation column of said gas chromatograph; a gauge pressure chamber also disposed within said housing and communicating with said carrier gas supply source; means for creating a pressure differential between said gauge pressure chamber and said liquid sample evaporation chamber; a first opening provided for said liquid sample evaporation chamber; a first gasket means made of an elastic material and disposed sealing said first opening; a second opening provided on said, gauge pressure chamber; a second gasket means of an elastic material sealing said second opening; a needle having both its ends pointed, said needle being bent to form two spaced substantially parallel limbs extending in the same direction, said needle having pointed ends to be introduced into said sample evaporation chamber and into said gauge pressure chamber, respectively, through said first and said second gasket means closing said first and said second opening; said needle having formed therein a longitudinal internal capillary extending substantially over the length of the needle and open at both said ends, said capillary being provided to be filled with said liquid sample, said limbs of the needle filled with the liquid sample being introduced into said sample evaporation chamber and said gauge pressure chamber respectively through said first and said second gasket means so that said first and second gasket means associated with said respective chambers are pierced simultaneously by the said respective pointed ends of said needle, thereby establishing conditions for transfer of said liquid sample from said passage of said needle into said sample evaporation chamber under the action of said pressure differential maintained between said gauge pressure chamber and said sample evaporation chamber.
 2. An apparatus according to claim 1, wherein said first and said second gasket means are formed by a unitary construction, common to both said gaskets.
 3. An apparatus according to claim 1, wherein said means for establishing a pressure differential between said gauge pressure chamber and said sample evaporation chamber includes a capillary passage establishing communication between said chambers.
 4. An apparatus according to claim 1, wherein said means for establishing a pressure differential between said gauge pressure chamber and said sample evaporation chamber includes a pressure differential regulator having an input pressure connection, a reference pressure connection and output pressure connection communicating, respectively, with said carrier gas supply source, with said sample evaporation chamber and with said gauge pressure chamber.
 5. An apparatus according to claim 1, wherein said gauge pressure chamber communicates with the ambient atmosphere through an additional capillary passage.
 6. An apparatus according to claim 1, wherein said needle has a bent portion thereof clamped into a holder so that said pointed limbs of the bent needle project from an end face of said holder by equal distances, parallel to each other. 